How to use cin with unknown input types?

Question

I have a C++ program which needs to take user input. The user input will either be two ints (for example: 1 3) or it will be a char (for example: s).

I know I can get th

Answer 1

You can do this in c++11. This solution is robust, will ignore spaces.

This is compiled with clang++-libc++ in ubuntu 13.10. Note that gcc doesn't have a full regex implementation yet, but you could use Boost.Regex as an alternative.

EDIT: Added negative numbers handling.

#include 
#include 
#include 
#include 


using namespace std;

int main() {
   regex pattern(R"(\s*(-?\d+)\s+(-?\d+)\s*|\s*([[:alpha:]])\s*)");

   string input;
   smatch match;

   char a_char;
   pair two_ints;
   while (getline(cin, input)) {
      if (regex_match(input, match, pattern)) {
         if (match[3].matched) {
            cout << match[3] << endl;
            a_char = match[3].str()[0];
         }
         else {
            cout << match[1] << " " << match[2] << endl;
            two_ints = {stoi(match[1]), stoi(match[2])};
         }
      }
   }
}